11991921 has 4 divisors (see below), whose sum is σ = 15989232. Its totient is φ = 7994612.

The previous prime is 11991913. The next prime is 11991937. The reversal of 11991921 is 12919911.

11991921 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 11991921 - 2³ = 11991913 is a prime.

It is not an unprimeable number, because it can be changed into a prime (11991911) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1998651 + ... + 1998656.

It is an arithmetic number, because the mean of its divisors is an integer number (3997308).

Almost surely, 2^11991921 is an apocalyptic number.

It is an amenable number.

11991921 is a deficient number, since it is larger than the sum of its proper divisors (3997311).

11991921 is an equidigital number, since it uses as much as digits as its factorization.

11991921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3997310.

The product of its digits is 1458, while the sum is 33.

The square root of 11991921 is about 3462.9353155957. The cubic root of 11991921 is about 228.8914583852.

The spelling of 11991921 in words is "eleven million, nine hundred ninety-one thousand, nine hundred twenty-one".